Weighting surface wave filters by withdrawing electrodes
AssigneeTexas Instruments Incorporated
InventorClinton S. Hartmann
Life of this patent
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Abstract
Prior art methods for shaping the impulse response of a surface wave delay line interdigital transducer include finger width weighting and finger overlap weighting. The new method for shaping the transducer impulse response disclosed herein overcomes several objectional characteristics of the prior art methods. The new method involves removal of individual fingers or groups of fingers from selected portions of the transducer. The amplitude of the impulse response in those regions from which fingers have been removed is reduced below the value which it would have if no fingers had been removed. The method thus provides the capability to control the relative amplitudes of the impulse response along the length of the transducer.
Claims18
A method for fabricating an acoustic surface wave interdigital transducer having an impulse response with predetermined relative amplitudes along the length thereof, said method comprising:
- defining the desired impulse response of the interdgital transducer to be fabricated,
- designing an interdigital transducer provided with opposed sets of overlapping fingers and having an impulse response with the same zero-crossings as the desired impulse response, and
- withdrawing one or more selected fingers from the designed interdigital transducer to produce an interdigital transducer having an impulse response approximating the desired response.
A method of fabricating an acoustic surface wave full-overlap interdigital transducer having an impulse response with predetermined relative amplitudes along the length thereof, said method comprising:
- defining the desired impulse response of the full-overlap interdigital transducer to be fabricated by a desired envelope function and a desired zero-crossing function,
- designing a full-overlap interdigital transducer provided with opposed sets of fully overlapping fingers and having an impulse response with the same zero-crossings as the desired impulse response, and
- withdrawing appropriate selected fingers from the designed full-overlap interdigital transducer so that the area under the envelope function of the full-overlap interdigital transducer and the area under said desired envelope function are equal over the full transducer length and approximately equal over any portion of the full transducer length in the full-overlap interdigital transducer which is produced.
An acoustic surface wave full-overlap interdigital transducer having an impulse reponse with predetermined relative amplitudes along the length thereof in approximation of a desired impulse response, said interdigital transducer comprising:
- opposed sets of overlapping fingers of equal length and width,
- said equal length interdigitated fingers being a subset of a set comprising an interdigitated finger corresponding to each zero-crossing of the desired impulse response, and
- said subset being selected so as to provide the approximation of the desired impulse response.
A method of fabricating an acoustic surface wave interdigital transducer having an impulse response with predetermined relative amplitudes along the length thereof, said method comprising:
- defining the desired impulse response of the interdigital transducer to be fabricated by at least a desired envelope function,
- designing an interdigital transducer provided with opposed sets of overlapping fingers and having an impulse response with an envelope function which is everywhere equal to or greater than that of the desired impulse response so as to produce an impulse response differing from but related to the desired impulse response, and
- withdrawing one or more selected fingers from predetermined locations on the designed interdigital transducer corresponding to positions on the envelope function which are greater than the respective positions on the envelope function of the desired impulse response to produce an interdigital transducer having an impulse response approximating the desired impulse response.
Dependencies are inferred from the claim text.